England's World Cup opener in Volgograd is a prime target for ISIS, experts have claimed

And with more than 400 hardliners now back in Russia, security experts believe ISIS radicals are planning to attack this summer’s tournament as an act for revenge for President Vladimir Putin’s air strikes in Syria.

Attacks are likely to be mounted against fans on match days using vans and knives or bomb blasts on busses and trains, with Moscow and St Petersburg also at risk.

Extremists are expected to attack Russia in response to Putin's backing of Assad in Syria

“Aspirational targets will include match day stadia, particularly in Moscow and St Petersburg – the two cities that will have the largest concentration of foreign visitors, with Moscow hosting the key fixtures of the World Cup, including the final and the opening fixture.

“Sochi and Volgograd are two other cities at heightened risk due to their proximity to the North Caucasus region meaning they are logistically viable cities for militants to stage attacks.”

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England will play their opening match against Tunisia in the city on 18 June but many Three Lions fans are expected to stay in either St Petersburg or Moscow and travel to group games by train or plane.

Manager Gareth Southgate will base his squad at a country hotel just outside St Petersburg, Russia’s second city and former capital.

The terror expert added that returning ISIS fighters posed as credible threat due to weapons and bomb-making experience, adding: “These fighters have had combat experience and have had training in operating military-grade firearms as well as manufacturing IEDS.”

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